System and method for testing contact quality of electrical-biosignal electrodes

ABSTRACT

One variation of a method for testing contact quality of electrical-biosignal electrodes includes: outputting a drive signal—including an alternating-current component oscillating at a reference frequency and a direct-current component—through a driven electrode; determining that a reference electrode is in improper contact with a user&#39;s skin if a reference signal read from the reference electrode excludes a first signal component oscillating at the reference frequency and a second signal component oscillating at an ambient frequency; determining that a sense electrode is in improper contact with the user&#39;s skin if the reference signal includes the first signal component and if a sense signal read from the sense electrode excludes a third signal component oscillating at the reference frequency; and generating an electrode adjustment prompt if one of the reference and sense electrodes is determined to be in improper contact with the user&#39;s skin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit of U.S. Provisional Application No.62/255,401, filed on 14 Nov. 2015, which is incorporated in its entiretyby this reference.

TECHNICAL FIELD

This invention relates generally to the field of electroencephalographyand more specifically to a new and useful system and method for testingcontact quality of electrical-biosignal electrodes in the field ofelectroencephalography.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flowchart representation of a method;

FIGS. 2A and 2B are flowchart representations of variations of themethod;

FIG. 3 is a schematic representation of a system;

FIG. 4 is a schematic representation of one variation of the system;

FIG. 5 is a schematic representation of one variation of the system; and

FIG. 6 is a flowchart representation of one variation of the method.

DESCRIPTION OF THE EMBODIMENTS

The following description of embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Variations, configurations, implementations, example implementations,and examples described herein are optional and are not exclusive to thevariations, configurations, implementations, example implementations,and examples they describe. The invention described herein can includeany and all permutations of these variations, configurations,implementations, example implementations, and examples.

1. Method

As shown in FIGS. 1, 2A, and 2B, a method for testing contact quality ofelectrical-biosignal electrodes includes: outputting a drive signalthrough a driven electrode no in Block S110, the drive signal includingan alternating-current component oscillating at a reference frequencyand a direct-current component; reading a reference signal from areference electrode 120 proximal the driven electrode 110 in Block S120;in response to the raw reference signal excluding a first signalcomponent oscillating at the reference frequency and excluding a secondsignal component oscillating at an ambient frequency, determining thatthe reference electrode 120 is in improper contact with a user's skin inBlock S122; in response to the raw reference signal excluding the firstsignal component oscillating at the reference frequency and includingthe second signal component oscillating at the ambient frequency,determining that the driven electrode 110 is in improper contact withthe user's skin in Block S124; reading a first sense signal from a firstsense electrode 131 in Block S130; in response to the raw referencesignal including the first signal component oscillating at the referencefrequency and in response to the first sense signal excluding a thirdsignal component oscillating at the reference frequency, determiningthat the first sense electrode 131 is in improper contact with theuser's skin in Block S132; and in response to determination of impropercontact between the user's skin and one of the driven electrode no, thereference electrode 120, and the first sense electrode 131, generatingan electrode adjustment prompt in Block S140.

2. Applications

Generally, the method S100 can be implemented by an electrical biosignalacquisition system 100 to systematically characterize the quality ofcontact between electrodes—in the electrical biosignal acquisitionsystem 100—and a user's skin and to automatically provide guidance forimproving such contact quality, such as to a technician overseeing theuser or to the user directly. In particular, the electrical biosignalacquisition system 100 executing the method S100 can output a drivesignal containing an AC component through the driven electrode 110 incontact with the user's skin and then determine the quality of contactbetween the user's skin and the driven electrode 110, the referenceelectrode 120, and a set of sense electrodes based on the presence of alike AC component in raw reference and sense signals collected by thereference and sense electrodes, respectively. The driven electrode nocan output a drive signal containing an AC component oscillating at afrequency distinct from a frequency of common ambient electromagneticnoise (e.g., 60 Hz continuous AC noise in North America, 50 Hzcontinuous AC noise in Europe) and unique to oscillating electricalsignals generated by a living (e.g., human) body such that alternatingcomponents in each of the raw reference and sense signals can becorrelated with (e.g., matched to) the AC component of the drivesignal—entering the body at the driven electrode 110—with a high degreeof accuracy. For example, the electrical biosignal acquisition system100 can output a drive signal containing a DC component between 1 Voltand 2 Volts and an AC component characterized by a sinusoidal, 2.0 Hz,17-millivolt peak-to-peak AC signal; and the electrical biosignalacquisition system 100 can correlate the presence of a 2.0 Hz AC signalin each of the raw reference and sense signals with the quality ofcontact between the user's skin and the reference and sense electrodes,respectively.

In one example, Blocks of the method S100 can be executed by anelectroencephalogram (EEG) headset including 19 sense electrodes, onedriven (e.g., “driven right leg”) electrode, and one reference electrode120, as described below, to determine whether the sense, driven, andreference electrode are in proper contact with a patient's skin duringadministration of an EEG test. In this example, the EEG headset 102 candrive the driven electrode 110 at a reference frequency of 2.0 Hz andcan determine: that the driven electrode 110 is in improper contact withthe patient's (i.e., a user's) skin in Block S124 when the raw referencesignal excludes a 2.0 Hz component but includes a 60 Hz component (acommon ambient electromagnetic noise signal in North America); that thereference electrode 120 is in improper contact with the patient's skinin Block S122 when the raw reference signal excludes both a 2.0 Hzcomponent and a 60 Hz component; and that a particular sense electrode131 is in improper contact with the patient's skin in Block S132 whenthe driven and reference electrode are determined to be in propercontact with the patient's skin and when a sense signal output by theparticular sense electrode 131 excludes a 2.0 Hz component (or whencomposite sense signal—including the raw reference signal subtractedfrom the raw sense signal—includes the 2.0 Hz component”). In thisexample, the EEG headset 102 can then broadcast a notification to anexternal connected device (e.g., a smartphone or tablet carried by anurse, doctor, therapist, or epileptologist, etc. administering the EEGtest) to notify an EEG test administrator of improper contact between aparticular electrode and the patient's skin (hereinafter a “contact lossevent”). In this example, the EEG headset 102 can additionally oralternatively flag or annotate data collected through each senseelectrode 131 during an EEG test with the determined contact states ofthe driven electrode 110, reference electrode 120, and sense electrodes.

The method S100 is described herein as executed by an EEG headset. Forexample, an EEG headset can execute Blocks of the method S100 to detectand actively handle contact loss events by notifying an EEG testadministrator of changes in contact quality at all or select electrodessubstantially in real-time. The EEG headset 102 can additionally oralternatively handle contact loss events passively by annotating datacollected by the sense (and reference) electrodes with contact lossevents. However, the method S100 can be similarly executed by anelectrocardiogram (ECG) system, an electromyogram (EMG) system, amechanomyogram (MMG) system, a electrooculography (EOG) system, agalvanic skin response (GSR) system, and/or a magnetoencephalogram(MEG), etc.

3. System

As shown in FIGS. 3, 4, and 5, the method S100 can be executed by anelectrical biosignal acquisition system 100, including: a drivenelectrode 110 electrically configured to contact skin of a user remotelyfrom an area of interest; a signal generator 140 configured to output adrive signal oscillating at a reference frequency about a center voltageinto the user via the driven electrode 110; a reference electrode 120configured to contact skin of the user remotely from the area ofinterest and to detect a raw reference signal; a first sense electrode131 configured to contact skin of the user at the area of interest andto detect a first raw sense signal from the area of interest; and asupport structure 104 configured to support the driven electrode 110,the reference electrode 120, and the first sense electrode 131 on theuser. The electrical biosignal acquisition system 100 also includes asignal processor 150 configured to: transform absence of a first signalcomponent oscillating at the reference frequency in the raw referencesignal and absence of a second signal component oscillating at anambient frequency from the raw reference signal into confirmation thatthe reference electrode 120 is in improper contact with the user's skin;transform absence of the first signal component oscillating at thereference frequency and presence of the second signal componentoscillating at the ambient frequency in the raw reference signal intoconfirmation that the driven electrode 110 is in improper contact withthe user's skin; and to transform confirmation that the referenceelectrode 120 is in proper contact with the user's skin, confirmationthat the driven electrode 110 is in proper contact with the user's skin,and absence of a third signal component oscillating at the referencefrequency from the first raw sense signal into confirmation that thefirst sense electrode 131 is in improper contact with the user's skin.(Similarly, the signal processor 150 can transform confirmation that thereference electrode 120 is in proper contact with the user's skin,confirmation that the driven electrode 110 is in proper contact with theuser's skin, and presence of a third signal component oscillating at thereference frequency in a first composite sense signal—representing adifference between the raw reference signal output by the referenceelectrode and the raw sense signal output by the first senseelectrode—into confirmation that the first sense electrode 131 is inimproper contact with the user's skin.)

The electrical biosignal acquisition system 100 is described herein asdefining an EEG headset 102 configured to collect neural oscillation (or“brain wave”) data from one or more sense electrodes when worn by auser. However, the electrical biosignal acquisition system 100 caninclude any other suitable type of biosensor electrode system. Theelectrical biosignal acquisition system 100 can also include one or morecontact-based or non-contact sensors and can implement methods andtechniques described herein to collect, process, and handle any suchcontact-based or non-contact sensor data.

4. Signal Generator and Driven Electrode

The signal generator 140 of the EEG headset 102 is configured to outputa drive signal that includes a DC component and an AC componentoscillating at a reference frequency; and the driven electrode no iselectrically coupled to the signal generator 140, is configured tocontact skin of a user, and outputs the drive signal into the user'sskin. Generally, the signal generator 140 generates a drive signal thatthe driven electrode no then communicates into the body of the user toestablish a known (or “reference”) potential at the user's body relativeto a power supply (e.g., a battery ground) within the EEG headset 102.

In one implementation, the EEG headset 102 includes a cage configured tosupport the driven electrode 110 against the user's skin but remotelyfrom the user's head where electrical signals from brain activity (i.e.,neural oscillations) predominate. For example, as shown in FIG. 5, thecage can include a beam extending downward from the top of the EEGheadset 102, supporting the driven electrode 110, and configured tocompress the driven electrode 110 against the right side of the user'sneck when the EEG headset 102 is worn by the user. Alternatively, thedriven electrode 110 can be mounted to the interior surface of a springclip and connected to the cage via a flexible hookup wire, and thespring clip can be manually opened and released onto the user's rightear lobe after the EEG headset 102 is installed on the user's head.

The EEG headset 102 can also include a battery 170, and the signalgenerator 140 and the battery 170 can be arranged within a housingsupported above or within the cage. The signal generator 140 can sourcecurrent from the battery 170, convert this current into a drive signaloscillating at a reference frequency about a center voltage (e.g., asinusoidal, 2.0 Hz, 17 millivolt peak-to-peak AC signal on a static ordynamic DC component between 0 and 3.3 Volts), and then output thisdrive signal to the driven electrode 110 via a hookup wire, as shown inFIG. 3. The signal generator 140 and the driven electrode 110 cantherefore cooperate to execute Block S110 of the method S100.

5. Reference Electrode

The reference electrode 120 is configured to contact skin of the userand to collect a reference signal from the user's body. Generally, thereference electrode 120 functions to conduct a reference signal from theuser's skin into the signal processor 150, which then analyzes the rawreference signal to confirm connectivity (e.g., contact) between theuser's skin and the driven electrode 110, the reference electrode 120,and one or more sense electrodes according to the method S100. Thesignal processor 150 within the EEG headset 102 can also implementcommon-mode rejection techniques to remove noise (e.g., artifacts) fromsense signals collected by the sense electrodes by subtracting the rawreference signal from each raw sense signal in Block S131, as describedbelow and shown in FIG. 2.

In one implementation, shown in FIGS. 3, 4, and 5, the referenceelectrode 120 includes a dry EEG electrode including: a substrate; a setof electrically-conductive prongs extending from a first side of thesubstrate; and an amplifier coupled to the substrate opposite the set ofprongs and configured to amplify an electrical signal detected by theset of prongs. The electrically-conductive prongs can be elastic (e.g.,gold-plated silicone bristles) or rigid (e.g., gold-plated copperprongs). The reference electrode 120 can alternatively include a flat ordomed contact disk configured to contact the user's skin. Alternatively,the reference electrode 120 can be configured to accept interchangeablecontact inserts, such as one of an elastic bristle insert, a rigid pronginsert, a flat contact disk insert, and a domed contact disk insert.

In this implementation, the amplifier can include a differential op-ampincluding: a non-inverting input electrically coupled to the substrate;and an inverting input that receives the DC component of the drivesignal from a DC output channel of the signal generator 140, as shown inFIG. 3. The amplifier can subtract the DC component of the drive signalfrom a high-impedance reference signal detected at the prongs, amplifythe result (e.g., by a gain of 10, 1,000, or 100,000), and output theamplified result as a low-impedance reference signal that follows thehigh-impedance reference signal less the DC component of the drivesignal and amplified by a gain value greater than 1. In thisimplementation, the output of the amplifier can be connected to thesignal processor 150, which can receive the low-impedance referencesignal from the reference electrode 120 and process this low-impedancereference signal to determine the contact state of the reference anddriven electrode, as in Blocks S122 and S124, respectively.

Alternatively, the reference electrode 120 can include a non-invertingop-amp in a closed-feedback configuration characterized by a gain of ˜1and including a non-inverting input electrically coupled to thesubstrate in the reference electrode 120. In this example, the amplifiercan include a buffer or a voltage follower (as shown in FIG. 4) and canreceive a high-impedance reference signal from the set of prongs andoutput a low-impedance reference signal that follows the high-impedancereference signal directly. However, the reference electrode 120 caninclude any other type of dry- or wet-type EEG electrode.

Like the driven electrode no described above, the EEG headset 102 cansupport the reference electrode 120 against the user's skin and remotelyfrom the user's head where electrical signals from brain activity aremost present. In particular, because the signal processor 150 removesthe raw reference signal from raw sense signals to form composite sensesignals, the EEG headset 102 can support the reference electrode 120against the user's skin substantially remotely from the sense electrodesand from the user's scalp, thereby minimizing collection of neuraloscillations (e.g., “brain waves”) by the raw reference signal, whichwould otherwise be rejected from the composite sense signals when theraw reference signal is subtracted from the raw sense signals in BlockS131, as described below. For example and as shown in FIGS. 1 and 5, thecase of the EEG headset 102 can include a second beam extending downwardfrom the top of the EEG headset 102, supporting the reference electrode120 opposite the driven electrode 110, and configured to compress thereference electrode 120 against the left side of the user's neck whenthe EEG headset 102 is worn by the user. Alternatively, like the drivenelectrode 110, the reference electrode 120 can be mounted to theinterior surface of a second spring clip and connected to the cage via asecond flexible hookup wire, and the second spring clip can be manuallyopened and released onto the user's ear left lobe after the EEG headset102 is installed on the user's head.

Therefore, the driven electrode 110 can output a drive signal—includingan AC component and a DC component—to establish a known, oscillatingpotential in the user's body during an EEG test in Block S110. When incontact with the user's skin during the EEG test, the referenceelectrode 120 detects the drive signal, ambient noise, and/or otherextraphysiologic artifacts and outputs these as a singular referencesignal to the signal processor 150 in Block S120.

6. Sense Electrode

The EEG headset 102 also includes a sense electrode 131 configured tocontact skin of the user and to pass neural oscillation data in the formof a sense signal from the user's skin into the signal processor 150. Inthe implementation described above in which the EEG headset 102 includesa cage, the cage can also support one or more sense electrodes 130 andcan compress the sense electrodes 130 against the user's scalp when theEEG headset 102 is worn on the user's head. For example, the EEG headset102 can include 19 sense electrodes 130 arranged in a 10-20configuration, including two sense electrodes supported across a frontalpolar site, four sense electrodes supported across a frontal lobeposition, four sense electrodes supported across a temporal lobeposition, five sense electrodes supported across lateral andlongitudinal center axes, two sense electrodes supported across aparietal lobe position, and two sense electrodes supported across anoccipital lobe position by the cage. However, the EEG headset 102 caninclude any other number of sense electrodes arranged in any otherformat or configuration.

Each sense electrode in the set of sense electrodes 130 can define a dryEEG electrode substantially similar to the reference electrode 120, suchas including: a substrate; a set of electrically-conductive prongsextending from a first side of the substrate; and an amplifier coupledto the substrate opposite the set of prongs and configured to amplify anelectrical signal passing through the set of prongs. Like the referenceelectrode 120 described above, when the EEG headset 102 is worn by theuser, a sense electrode 131 can: contact the user's scalp; detect ahigh-impedance sense signal from the user's skin; convert thehigh-impedance sense signal into a low-impedance sense signal less theDC component of the drive signal (e.g., at a differential op-amp); andpass the low-impedance sense signal to the signal processor 150. The setof sense electrodes 130 can therefore be substantially similar, and eachsense electrode 131 can be substantially similar to the referenceelectrode 120 such that the group of reference and sense electrodesoutput signals exhibiting similar gains, latencies, extraphysiologicartifacts, and/or intraphysiologic artifacts, etc.

However, the EEG headset 102 can include any other number and type ofdry or wet sense electrodes.

7. Signal Processor

The EEG headset 102 also includes a signal processor 150 configured to:subtract a component of a raw reference signal output by the referenceelectrode 120 from a raw sense signal output by the sense electrode 131to calculate a composite sense signal for the sense electrode 131 inBlock S131; and to determine quality of contact between the drivenelectrode 110, the reference electrode 120, and each sense electrode 131in the set of sense electrodes 130 based on the presence of componentsoscillating at the ambient frequency in the raw reference signal andbased on presence of components oscillating at the reference frequencyin the raw reference signal and in the sense signals. Generally, thesignal processor 150 functions: to receive a raw reference signal fromthe reference electrode 120 and a raw sense signal from each of one ormore sense electrodes in Blocks S120 and S130, respectively; todetermine connectivity between the user's skin and the driven andreference electrode based on stability (or presence) of one or more ACcomponents in the raw reference signal in Blocks S124 and S122,respectively; and—once the drive and reference electrodes are determinedto be in proper contact with the user's skin—to determine connectivitybetween the user's skin and a sense electrode 131 based on the presenceof an AC component characterized by the reference frequency in acorresponding raw sense signal (or absence of the AC component acorresponding composite sense signal) in Block S132.

In one implementation, the signal processor 150 includes an(multi-channel) analog-to-digital converter (ADC) that transforms a raw,low-impedance analog reference signal received from the referenceelectrode 120 into a raw digital reference signal (i.e., a digital valuerepresenting a voltage on the output channel of the reference electrode120 for each sampling period). The signal processor 150 then computes afrequency (e.g., Fourier) transform of the digital reference signal,such as for a sampling period including one, two, four, or other numberof cycles of the reference frequency. For example, for a referencefrequency of 2.0 Hz, the signal processor 150 can compute the Fouriertransform of the digital reference signal over a 1.33-second samplingperiod, which may include two cycles of the AC component of the drivesignal if the driven and reference electrode are in proper contact withthe user's skin. In particular, if the frequency transform of thedigital reference signal includes an AC component at the referencefrequency, the signal processor 150 can determine that the driven andreference electrode are properly coupled via the user's skin and aretherefore in proper contact with the user's skin for the samplingperiod. However, if the frequency transform of the digital referencesignal excludes an AC component at the reference frequency, the signalprocessor 150 can determine that the driven and reference electrode arenot properly coupled through the user and therefore that either or boththe driven electrode no and the reference electrode 120 are not inproper contact with the user's skin.

In the foregoing implementation, if the frequency transform of thedigital reference signal excludes both a first AC component at thereference frequency and a second AC component characterized by a commonambient electromagnetic noise frequency (e.g., 60 Hz in North America),the signal processor 150 can determine that the reference electrode 120is in improper contact with the user's skin in Block S122. For example,the user's body may function as an RF collector (e.g., an “antenna”)that collects ambient electromagnetic noise and communicates thiselectromagnetic noise into the reference electrode 120 when thereference electrode 120 is in proper contact with the user's skin.Therefore, for the EEG headset 102 used indoors in a lighted room inNorth America, if an oscillating (e.g., sinusoidal) 60 Hz signalcomponent is not detected in the digital reference signal, the signalprocessor 150 can determine that (at least) the raw reference signal isin improper contact with the user's skin in Block S122.

However, if the frequency transform of the digital reference signalexcludes an AC component at the reference frequency but includes an ACcomponent at a frequency of persistent ambient electromagnetic noise,the signal processor 150 can determine that the driven electrode 110 isin improper contact with the user's skin in Block S124. In particular,for the EEG headset 102 used indoors in a lighted room in North America,if the reference electrode 120 is in proper contact with the user's skinbut the driven electrode 110 is not, the digital reference signal mayinclude a sinusoidal 60 Hz signal component but may exclude an ACcomponent like the AC component output by the drive signal. The signalprocessor 150 can therefore determine the contact state of the drivenelectrode 110 in Block S124 based on the presence of (or lack of)certain AC signals in the raw reference signal.

For each sampling period during an EEG test, the ADC can also transforma raw, low-impedance analog sense signal received from a sense electrode131 into a raw digital sense signal (i.e., a digital value representinga voltage on the output channel of the sense electrode 131 for eachsampling period). The signal processor 150 can then subtract a digitalvalue (e.g., a 32-bit value) of the digital reference signal from adigital value (e.g., also a 32-bit value) of the digital sense signalfor the same sampling period to calculate a composite digital sensesignal representing a voltage at the input side of the sense electrode131 (i.e., a neural voltage relative to the reference signal) for thesampling period in Block S131. The signal processor 150 can repeat thisprocess for each sense electrode 131 to calculate one composite digitalsense signal per sense electrode 131 per sampling period during the EEGtest.

Alternatively, the signal processor 150 can subtract the raw,low-impedance analog reference signal from the raw, low-impedance analogsense signal to calculate a composite analog sense signal in Block S131and then pass this composite analog sense signal through the ADC. Forexample, each sense electrode 131 can include a differential op-amp:including an inverting input electrically connected to the output of thereference electrode 120; a non-inverting input electrically connected tothe output of the sense electrode 131; and an output feeding into onechannel of the ADC. In this example, the ADC can thus transform anoutput of the differential op-amp connected to the sense electrode 131(i.e., a “composite analog sense signal”) directly into a compositedigital sense signal. The signal processor 150 can repeat this processfor each sense electrode 131 to calculate one composite digital sensesignal per sense electrode 131 per sampling period during the EEG test.

Because the raw reference signal and a raw sense signal output by aparticular sense electrode 131 may include common ambient noise andother extraphysiologic and/or intraphysiologic artifacts, the signalprocessor 150 can achieve common-mode rejection by subtracting the rawreference signal (in raw low-impedance analog form or in raw digitalform) from the raw sense signal for the particular sense electrode 131in Block S131, thereby improving the signal-to-noise ratio (SNR) foreach sense channel. Furthermore, because the reference electrode 120 isconfigured to contact the user's skin remotely from the scalp or otherregion of the user's head in which neural oscillations are commonlypresent (or present in greater amplitude), the raw reference signal mayexclude a neural oscillation component or include only a very minorneural oscillation component such that neural oscillations in thecomposite sense signal are not rejected when the raw reference signal issubtracted from the sense signal in Block S131.

For each sense electrode 131, the signal processor 150 can then computea frequency transform of the composite digital sense signal (e.g., for asequence of composite digital sense signals over a period of time). Inthis implementation, if the driven and reference electrode aredetermined to be in proper contact with the user's skin, as describedabove, and if the frequency transform of the composite digital sensesignal corresponding to a particular sense electrode 131 excludes an ACcomponent at the reference frequency, the signal processor 150 candetermine that the particular sense electrode 131 is in proper contactwith the user's skin for the sampling period. In particular, the drivenand sense electrodes couple via the user's body when both are in propercontact with the user's skin; the raw, low-impedance sense signal outputby the sense electrode 131 therefore includes an AC component at thereference frequency when the drive and sense electrodes are in propercontact. When the reference electrode 120 is also in proper contact withthe user's skin, the low-impedance reference signal output by thereference electrode 120 similarly includes an AC component at thereference frequency; therefore, when the low-impedance reference signalis subtracted from the raw, low-impedance sense signal in Block S131 andthe result converted to digital form, the resulting composite digitalsense signal excludes an AC component at the reference frequency. Inparticular, in Block S136, the signal processor 150 can determine that asense electrode is in proper contact with the user's skin when: properskin contact at the driven electrode is confirmed in Block S126; properskin contact at the reference electrode is confirmed in Block S126; andthe frequency transform of the composite digital sense signal of thesense electrode—calculated by subtracting the low-impedance referencesignal from the low-impedance sense signal and digitizing the result inBlock S131—excludes an AC component at the reference frequency, as shownin FIG. 2A.

However, if the driven and reference electrode are determined to be inproper contact with the user's skin and the frequency transform of thecomposite digital sense signal includes an AC component characterized bythe reference frequency (which will be phased 180° from the AC componentof the drive signal), the signal processor 150 can determine that thesense electrode 131 is not in proper contact with the user's skin inBlock S132, as shown in FIG. 2A. In particular, when the sense electrode131 is not in proper contact with the user's skin, the raw,low-impedance sense signal output by the sense electrode 131 excludes anAC component at the reference frequency. When the reference electrode120 is in proper contact with the user's skin, the low-impedancereference signal output by the reference electrode 120 does include anAC component at the reference frequency; when the raw, low-impedancereference signal is then subtracted from the raw, low-impedance sensesignal in Block S131 and the result digitized, the resulting compositedigital sense signal includes an AC component at the reference frequencybut phased at 180° from the drive signal, which the signal processor 150can then interpret as improper contact between the user's skin and thesense electrode 131 in Block S132, as shown in FIG. 2A.

Therefore: an amplifier integrated into the reference electrode 120 canoutput a low-impedance reference signal that follows a high-impedancereference signal detected by prongs (or other contact surface) on thereference electrode 120; and the signal processor 150 can subtract a DCcomponent of the drive signal from the low-impedance reference signaland represent this difference in a composite digital reference signal(e.g., as one digital value per sampling period) in Block S131. Thesignal processor 150 can then decompose the composite digital referencesignal into a first set of oscillating signal components, such as byimplementing frequency analysis techniques substantially in real-time toprocess a set of digital values representing the composite digitalreference signal over a contiguous sequence of sampling periods. Thesignal processor 150 can then determine that the reference electrode 120is in improper contact with the user's skin in Block S122 if the firstset of oscillating signal components excludes both a first signalcomponent oscillating at the reference frequency (e.g., 2 Hz) and asecond signal component oscillating at an ambient frequency (e.g.,approximately 60 Hz in North America, 50 Hz in Europe). Similarly, thesignal processor 150 can determine that the driven electrode 110 is inimproper contact with the user's skin in Block S124 if the first set ofoscillating signal components excludes the first signal componentoscillating at the reference frequency but includes the second signalcomponent oscillating at the ambient frequency. However, the signalprocessor 150 can determine that the driven electrode 110 and thereference electrode 120 are in proper contact with the user's skin inBlock S126 if the first set of oscillating signal components—extractedfrom the digital reference signal—includes the first signal componentoscillating at the reference frequency.

Furthermore: an amplifier integrated into a sense electrode 131 canoutput a raw, low-impedance sense signal that follows a raw,high-impedance sense signal detected by prongs (or a contact surface) onthe sense electrode 131; and the signal processor 150 can subtract theraw, low-impedance reference signal from the raw, low-impedance sensesignal in Block S131 and digitize this difference to create a compositedigital sense signal. (The signal processor 150 can alternativelysubtract one digital reference value of a raw digital reference signalfrom a digital sense value of a raw digital sense signal recorded duringthe same sampling period for each sampling period during operation ofthe EEG headset 102 to create a composite digital sense signal for thissense electrode in Block S131.) The signal processor 150 can thendecompose the composite digital sense signal into a second set ofoscillating signal components, such as by implementing frequencyanalysis techniques in real-time to process a set of digital valuesrepresenting the composite digital sense signal over a contiguoussequence of sampling periods. Once the signal processor 150 determinesthat the drive and reference electrode are in proper contact with theuser's skin, the signal processor 150 can then determine that the senseelectrode 131 is in improper contact with the user's skin in Block S132if the second set of oscillating signal components includes a thirdsignal component oscillating at the reference frequency (i.e., a thirdsignal component oscillating at the reference frequency and phased at180° from the AC component of the drive signal due to subtraction of theraw reference signal—containing a signal component oscillating at thereference frequency and in-phase within the drive signal—from the rawsense signal). However, the signal processor 150 can also determine thatthe sense electrode 131 is in proper contact with the user's skin inBlock S136 if the second set of oscillating signal components excludesthe third signal component oscillating at the reference frequency.

The signal processor 150 can test the skin connectivity of the drivenelectrode 110, the reference electrode 120, and the set of senseelectrodes 130 serially and continuously throughout operation (e.g.,throughout an EEG test), as shown in FIGS. 2A and 2B. A controller 160can then handle detected loss of skin contact for all or a subset ofelectrodes in the EEG headset 102, as described below.

8. Controller

One variation of the EEG headset 102 further includes a controller 160that handles instances of improper or poor contact between the user'sskin and any of the drive, reference, and sense electrodes duringoperation (or “contact loss events”). Generally, the controller 160 canexecute Block S140 of the method S100, which recites: in response todetection of improper contact between the user's skin and one of thedriven electrode 110, the reference electrode 120, and the senseelectrode 131, broadcasting an electrode adjustment prompt to anexternal device.

8.1 Push Notifications

In one implementation, the EEG headset 102 also includes a wirelesscommunication module 162, as shown in FIG. 3, configured to communicatewirelessly (e.g., directly or through a network, such as through theInternet or over a cellular network) with a smartphone, tablet,smartwatch, or other external wireless-enabled device carried oraccessible by a nurse, doctor, therapist, epileptologist, or other EEGtest administrator administering an EEG test with the EEG headset 102 tothe user. Before initiating an EEG test, the wireless communicationmodule 162 can connect wirelessly to an external device and can maintaina persistent wireless connection with the external device during the EEGtest. During the EEG test, the controller 160 can push notifications forcontact loss events, as described below, to the external devicesubstantially in real-time in order to prompt the EEG test administratorto quickly correct electrode contact issues. For example, the controller160 can push a notification in the form of a SMS text message or anin-application notification to the external device.

The external device can additionally or alternatively execute a nativeEEG test application including a virtual graphical representation of theEEG headset 102 and the drive, reference, and sense electrodes. In thisimplementation shown in FIG. 6, the controller 160 can push electrodestatus updates to the external device—such as via a short-range wirelesscommunication protocol—substantially in real-time or in response to achange in the contact status of an electrode. Upon receipt of an updatefrom the EEG headset 102, the native EEG test application can update thevirtual graphical representation of the EEG headset 102 accordingly inorder to visually indicate the contact status of each electrode. Thenative EEG test application can then serve audible, visual, and/orhaptic prompts to the EEG test administrator to correct fitment of aparticular electrode on the user's scalp when a predefined trigger eventis detected, as described below.

The controller 160 can therefore selectively push notifications to theexternal device in response to detected contact loss events in BlocksS122, S124, and S132. Alternatively, the native EEG test applicationexecuting on the external computing device can regularly pull contactstates of electrodes in the EEG headset 102, such as once per second oronce per five-second interval, and implement methods and techniquesdescribed above and below to selectively serve prompts to the EEG testadministrator to correct skin contact at one or more electrodes in theEEG headset.

8.2 Electrode Adjustment Prompt

In one implementation, in response to a contact loss event, thecontroller 160 generates a notification that: identifies a specificelectrode that has lost contact with the user's skin; includes anidentifier of the EEG headset 102 worn by the user; and includes atextual and/or graphical prompt to restore proper contact between theuser's skin and the identified electrode by adjusting the EEG headset102. For example, if the driven electrode 110 is determined to be inimproper contact with the user's skin in Block S124, the controller 160can generate a notification including a graphical representation of theEEG headset 102 including the electrodes, can highlight the drivenelectrode 110 (e.g., in red) in the graphical representation of the EEGheadset 102, and can overlay a textual prompt reciting “Please depressthe driven electrode no on the right side of the patient's neck untilproper body contact is restored” over the graphical representation ofthe EEG headset 102.

In another implementation, the controller 160 can: generate anelectronic notification containing a prompt to correct contact between aparticular electrode—in the set of electrodes—determined to be out ofcontact with the user's skin (or out of contact with the user's skin formore than a threshold period of time); insert a virtual map of locationsof the set electrodes in the EEG headset 102 into the electronicnotification; and indicate the particular electrode within the virtualmap in Block S140. For example, if a Fp1 sense electrode 131 isdetermined to be in improper contact with the user's skin in Block S132,the controller 160 can: generate a notification including a graphicalrepresentation of the EEG headset 102 representing general positions ofelectrodes; highlight the Fp1 electrode (e.g., in red) in the graphicalrepresentation of the EEG headset 102; and insert a textual promptreciting “Please tighten the front adjustable headband on the headsetuntil contact at the Fp1 electrode is restored” over the graphicalrepresentation of the EEG headset 102 in Block S140.

In a similar implementation, each electrode in the EEG headset 102 canbe color-coded (or patterned) with a color (e.g., or pattern) uniquewithin the set of electrodes, and, in response to a contact loss eventat a particular electrode, the controller 160 can generate a contactloss notification identifying the particular electrode by its uniquecolor (or pattern). However, the controller 160 and/or the externaldevice can implement any other method or technique to notify an EEG testadministrator of a contact loss event.

8.3 Notification Timing

In this implementation, the controller 160 can also delay transmissionof a notification of a contact loss event at a particular electrodeuntil the particular electrode has been out of proper contact with theuser's skin for at least a threshold duration, a custom durationselected by the EEG test administrator, or a duration proportional tothe physical distance between the user and the EEG test administrator.For example, the controller 160 can track a duration of a contiguousperiod of time during which a first sense electrode 131 is determined tobe in improper contact with the user's skin; and then transmit anelectronic notification prompting adjustment of the first senseelectrode 131 to an external device accessible by anelectroencephalography test administrator if the duration of thecontiguous period of time exceeds a threshold duration, such as fiveseconds. In a similar example, the controller 160 can track a totalduration of time over which the first sense electrode 131 is determinedto be in improper contact with the user's skin since a last manualadjustment of the EEG headset 102 or within a preset interval (e.g., oneminute, five minutes); and then transmit an electronic notificationprompting adjustment of the first sense electrode 131 to the externaldevice in Block S140 if the total duration of time exceeds a thresholdduration, such as twenty seconds since the EEG headset 102 was lastadjusted by the EEG test administrator or ten seconds within a lastone-minute interval.

In another example, the controller 160 can track a total duration oftime during which sense electrodes across the set of sense electrodes130 are determined to be in improper contact with the user's skin (i.e.,a sum of the total time that each sense electrode 131 has been out ofcontact with the user's skin), such as since a last manual adjustment ofthe EEG headset 102 or within a preset interval; and then transmit, tothe external device, a second electronic notification prompting restartof the current EEG test substantially in real-time when this totalduration of time exceeds a second threshold duration (e.g., one minute,one minute within the last five minutes, or 5% of the total sensed timeacross the set of sense electrodes). (In a similar example, thecontroller 160 can determine asynchronously that insufficient data wascollected through electrodes during the EEG test, such as if the ratioof total time that a sense electrode 131 was in improper contact withthe user's skin to the total recorded data stream time across 19 senseelectrodes exceeds 5%, and then prompt the EEG test administrator torepeat the EEG test following its conclusion.) The controller 160 cantherefore selectively push a notification to an EEG test administrator(e.g., to a smartphone carried by the EEG test administrator or toanother external device accessible to the EEG test administrator) whenan amount of time that a single sense electrode 131 has been out ofcontact with the user's skin or when a total amount of time that senseelectrodes in the set have been out of contact with the user's skinexceeds a preset threshold time.

The controller 160 can implement similar methods and techniques to pushsuch a notification to the EEG test administrator if either the drivenelectrode 110 or the reference electrode 120 is determined to be out ofcontact with the user's skin. For example, because improper contactbetween the user's skin and either the driven electrode 110 or thereference electrode 120 may produce raw (or composite) sense signalsthat are unusable, the controller 160 can implement shorter thresholdtimes to trigger transmission of an electrode adjustment prompt to theEEG test administrator following detection of improper skin contact atthe drive and sense electrodes, such as: a contiguous two seconds ofimproper contact; five seconds of improper contact since a last manualadjustment of the EEG headset 102; or five seconds within a five minuteinterval.

8.4 Filtered Notifications

In a similar variation, the controller 160 responds to contact lossevents by selectively pushing notifications to the EEG testadministrator. In this variation, the controller 160 can withholdcontact loss notifications from an EEG test administrator based on atype of electrode that has lost contact, a total number of electrodesnot in proper contact at a particular instant in time, a total durationof time that one or a group of electrodes have been in improper contactwith the user's skin (as described above), and/or a type of EEG testbeing administered to the user, etc.

In one implementation, for a general EEG test in which the EEG headset102 is configured to record data from all channels (e.g., all 19electrodes in a 10-20 headset configuration) in the EEG headset 102, thecontroller 160 can push contact loss notifications to an EEG testadministrator substantially in real-time if either the driven electrode110 or the reference electrode 120 is determined to have lost contactwith the user's skin. However, the controller 160 can delay notifyingthe EEG test administrator of contact loss events at sense electrodesuntil a total number of sense electrodes simultaneously not in contactwith the user's skin surpasses a threshold electrode count (e.g., twoelectrodes, three electrodes). In one example, the controller 160 canimplement a static, preset threshold electrode count, or the thresholdelectrode count can be customized by the EEG test administrator, such asthrough the native EEG test application executing on an external device,such as a smartphone or tablet carried by the EEG test administrator. Inanother example, the controller 160 can dynamically adjust the thresholdnumber of electrodes based on a physical distance between the EEGheadset 102 and the external device. In this example, the controller 160and the wireless communication module 162 can cooperate to implementtime-of-flight techniques to estimate the distance between the EEGheadset 102 and the external device, and the controller 160 can adjustthe threshold electrode count—to trigger prompting the EEG testadministrator to correct a position of the EEG headset 102—proportionalto this determined distance. In this example, the controller 160 can setthe threshold electrode count to: null (i.e., zero electrodes) for adistance of less than five feet between the EEG headset 102 and theexternal device; one electrode for a distance of five feet to ten feetbetween the EEG headset 102 and the external device; two electrodes fora distance of ten feet to thirty feet between the EEG headset 102 andthe external device; three electrodes for a distance greater than thirtyfeet between the EEG headset 102 and the external device.

In another implementation, the controller 160 can deactivate selectsense electrodes during all or a portion of an EEG test and canbroadcast contact loss notifications only for contact loss events atelectrodes that are active during the EEG test. For example, the nativeEEG test application—executing on the external device that is pairedwith the EEG headset 102—can include a set of preconfigured EEG testtypes, each EEG test type specifying a test duration and a group ofsense electrodes that are active throughout the test duration. In thisexample, the native EEG test application can store a set ofpreconfigured EEG test types and parameters, including: a full EEG testtype specifying a 40-minute duration with all 19 sense electrodes active(i.e., relevant to the full EEG test); a frontal lobe test typespecifying a 20-minute duration with sense electrodes at the fivefrontal lobe positions (e.g., FZ, F3, F7, F4, and F8) and the twofrontal polar sites (e.g., Fp1 and Fp2) active and all other senseelectrodes inactive; and a right-temporal lobe test type specifying a15-minute duration and the two right-temporal lobe sense electrodes(e.g., T4 and T6) active and all other sense electrodes inactive; etc.

In the foregoing example, the native EEG test application can alsoenable an EEG test administrator (or a neurologist, etc.) to design orconfigure a custom EEG test, such as a custom EEG test specifying acustom subset of occipital lobe, frontal lobe, parietal lobe, and centerposition sense electrodes as active for a custom duration. Furthermore,the native EEG test application can enable the EEG test administrator(or a neurologist, etc.) to design or configure a dynamic EEG test inwhich a subset of active sense electrodes changes throughout theduration of the custom EEG test, such as based on time from start of theEEG test or based on artifacts or neural oscillations recorded duringthe EEG test. Furthermore, through the native EEG test application, theEEG test administrator can select a standard EEG test from apre-populated list of EEG tests, modify an existing EEG test, orconfigure a custom EEG test for an upcoming EEG test period, and theexternal device executing the native EEG test application can uploadparameters of the selected EEG test to the EEG headset 102 (e.g., theduration of the EEG test, identifiers or addresses of active senseelectrodes), such as over short-range wireless communication protocol inpreparation for execution of a new EEG test by the EEG headset 102.During execution of the EEG test at the EEG headset 102, the controller160 can implement definitions of “active” sense electrodes noted in theEEG test parameters to selectively filter contact loss events and toselectively issue notifications to the EEG test administrator (or to theuser, etc.) to correct contact between these active sense electrodes andthe user's skin. In particular, the controller 160 can: generate aprompt specifying adjustment of a first sense electrode 131 defined asrelevant (or “active”) for a type of the electroencephalography testcurrently underway at the EEG headset 102 in response to determinationof improper contact between the user's skin and the first senseelectrode 131 and then serve this prompt to the EEG test administrator,as described above; while also disregarding determination of impropercontact between the user's skin and a second sense electrode 132 definedas irrelevant (or “inactive”) for the type of electroencephalographytest currently underway at the EEG headset 102.

Alternatively, the controller 160 can set the signal processor 150 todeactivate (e.g., “ignore”) sense channels for sense electrodesdesignated as inactive (or not designated as active) during the EEGtest; the signal processor 150 can therefore not test inactive senseelectrodes for proper skin contact during the EEG test.

Yet alternatively, the signal processor 150 can continue to processsense signals from the inactive sense electrodes and predict futurecontact states at active sense electrodes based on determined skincontact states at inactive sense electrodes. For example, poor contactat an Fp1 electrode in a 19-sense-electrode EEG headset may beindicative of poor skin contact—in the near future—at the Fp2 electrode(and vice versa). In this example, when executing a right-frontal-lobeEEG test in which sense signals from the Fp2, F4, and F8 electrodes arerecorded exclusively, the controller 160 can preempt contact loss at theFp2 by prompting the EEG test administrator to check the Fp2 electrodeif poor contact is detected at the Fp1 electrode, such as despitedetermination that the Fp2 electrode is currently in proper contact withthe user's skin. In this implementation, the controller 160 (or thenative EEG test application described above), can thus implement avirtual model of a mechanical structure of the EEG headset 102 and/or amodel or lookup table defining relationships between contact loss eventsat electrodes across the EEG headset 102 to predict future contact lossevents at active electrodes based on contact states of inactiveelectrodes.

Similarly, when prompting the EEG test administrator to correct contactat a particular (active) electrode due to contact loss at the particularelectrode, the controller 160 can also prompt the EEG test administratorto check other (active) electrodes—currently determined to be in propercontact but that exhibit contact loss linked to contact loss at theparticular electrode (e.g., as defined in the virtual model of the EEGheadset 102)—for proper contact when correcting the particularelectrode.

Yet alternatively, the signal processor 150 can process (raw orcomposite) sense signals from all sense electrodes and issue flags forcontact loss events for all sense electrodes, and the controller 160 cangenerate and transmit notifications for contact loss events at only theactive sense electrodes and discard (e.g., ignore) contact loss eventsfor inactive sense electrodes. However, the signal processor 150 and thecontroller 160 can cooperate in any other way to selectively activateand deactivate sense electrodes (or sense channels) and to selectivelyissue notifications for contact loss events at active sense electrodesduring an EEG test. The native EEG test application can similarlyselectively update a graphical representation of the EEG headset 102 toindicate contact states or contact loss events at active electrodes onlyand can selectively serve relevant prompts to the EEG test administrator(or to the user directly, as described below).

8.5 Adjustment Directives

In another variation, in Block S140, the controller 160 populates aprompt to correct skin contact at a particular electrode with adescription of a preferred or suggested mode of correction at theparticular electrode. In one implementation, in response to detection ofimproper contact between a first sense electrode 131 and the user'sskin, the controller 160: predicts an adjustment mode for the EEGheadset 102 to improve contact between the first sense electrode 131 andthe user's skin based on a virtual model of a mechanical structure ofthe EEG headset 102; inserts a description of the adjustment mode intoan electronic notification; and transmits the electronic notification toa local computing device.

In one example in which the EEG headset 102 includes a lower-rearheadband supporting T3, T5, O1, O2, T6, and T4 electrodes, if the signalprocessor 150 determines that at least three of these six electrodes onthe lower-rear headband are in improper contact at a particular instantin time or are exhibiting fluctuating contact states, the controller 160can: predict that the lower-rear headband is loose on the user's headbased on a virtual model of a mechanical structure of the EEG headset102, as described above; insert a prompt to tighten the lower-rearheadband into an electronic notification; and then transmit theelectronic notification to the external device for response by the EEGtest administrator. In a similar example, the EEG headset 102 includes:a lower-rear headband supporting T3, T5, O1, O2, T6, and T4 electrodes;a lower-front headband supporting F7, Fp1, Fp2, and F8 electrodes; acenter headband supporting C3, CZ, and C4 electrodes; and a center-frontheadband supporting F3, FZ, and F4 electrodes. In this example, if thesignal processor 150 determines that at least one of the C3, CZ, and C4electrodes and at least one of the F3, FZ, and F4 electrodes are inimproper contact at a particular instant in time or are exhibitingfluctuating contact states, the controller 160 can: predict that eitherthe lower-rear headband or the front-lower headband is too tight on theuser's head; insert a prompt to loosen the lower-rear and lower-frontheadbands into an electronic notification; and then transmit theelectronic notification to the external device for response by the EEGtest administrator.

In another example, the controller 160 can access a set of templateimages of contact states across electrodes in a like EEG headset,wherein each template image defines a (unique) combination of electrodesin proper and improper contact and is associated with a particularadjustment mode to correct electrodes in improper contact. In thisexample, the controller 160 can match an image of current contact statesacross electrodes in the EEG headset 102 to a particular template image,insert a description of the adjustment mode stored with the matchedtemplate image into an electronic notification, and then serve thisnotification to the EEG test administrator.

The controller 160 can thus implement: a virtual model of a mechanicalstructure of the EEG headset 102; a model or lookup table definingrelationships between contact states of groups of electrodes andadjustment of the support structure of the EEG headset 102; or astatistical model or table of common causes of contact loss events ofspecific electrodes; etc. to predict adjustment modes that will correctloss of skin contact at one or more electrodes in the EEG headset 102and then serve an electrode adjustment prompt containing a descriptionof this adjustment mode to the EEG test administrator in order tostreamline and guide manual adjustment of the EEG headset 102 inreal-time during an EEG test. However, the controller 160 (or the nativeEEG test application, etc.) can implement any other method or techniqueto transform the contact states of one or more electrodes in the EEGheadset 102 into a directed prompt to correct skin contact at theseelectrodes.

The controller 160 can also implement tiered adjustment modes whenserving guidance to the EEG test administrator for correct skin contactat an electrode. For example, for the reference electrode 120 determinedto be in poor contact with the user's skin (e.g., the user's rightearlobe or the right side of the user's neck), the controller 160 cansequentially serve guidance to the EEG test administrator to: jostle thereference electrode 120; then clean the user's skin at the location ofthe reference electrode 120 if poor skin contact persists afterjostling; then exchange a disk-shaped electrode tip for a bristleelectrode tip at the reference electrode 120 if poor skin contactpersists after cleaning; and finally to replace the reference electrode120 entirely if poor skin contact persists after exchanging electrodetips. In this example, the controller 160 can receive confirmation fromthe EEG test administrator that such guidance was followed andattempted, such as through the native EEG test application andsequentially step through such preplanned adjustment modes specific tothe reference electrode 120 (or generic to all electrodes in the EEGheadset 102). The controller 160 can also transmit updated notificationsor electrode contact states to the external device for presentation tothe EEG test administrator substantially in real-time. The controller160 can additionally or alternatively update lighted indicators(described below) integrated into the headset to visually indicatecontact states of the electrodes substantially in real-time. However,the controller 160 can serve any other guided and/or tiered prompts tothe EEG test administrator (or to the user directly) in any othersuitable way in Block S140.

8.6 Integrated Contact Quality Indicator

In one variation, the EEG headset 102 further includes a lightedindicator 164 adjacent each electrode and updates a state of eachlighted indicator 164 according to the contact state of itscorresponding electrode. For example, each electrode can include a red(i.e., single-color) LED opposite its set of prongs and electricallycoupled to a corresponding LED driver within the controller 160. In thisexample, the controller 160 can activate (i.e., turn ON) an LED in aparticular electrode when the particular electrode is determined to havelost contact with the user's skin in Block S122, S124, or S132. Inanother example, each electrode can include a multi-color LED oppositeits set of prongs; for each electrode in the EEG headset 102, thecontroller 160 can set the color of an LED on an electrode: to green ifcontact between the user's skin and the electrode is determined to beproper; to red if contact between the user's skin and the electrode isdetermined to be improper; and to yellow if contact between the user'sskin and the electrode is fluctuating between proper and improper (e.g.,at a rate between 0.1 Hz and 2 Hz). In a similar example, each electrodecan include a discrete red LED and a discrete, adjacent green LEDopposite its set of prongs; for each electrode in the EEG headset 102,the controller 160 can activate either the red LED or the green LEDbased on the skin contact state of the electrode.

In this variation, in Block S140, the controller 160 can: illuminate afirst lighted indicator—arranged in the EEG headset 102 adjacent thefirst sense electrode 131—in a first color to indicate improper contactbetween the user's skin and the first sense electrode 131 in response todetermination of improper contact between the user's skin and the firstsense electrode 131 in Block S132; and can illuminate a second lightedindicator—arranged in the EEG headset 102 adjacent the second senseelectrode 132—in a second color to indicate proper contact between theuser's skin and the second sense electrode 132 in response todetermination of proper contact between the user's skin and the secondsense electrode 132 in Block S136. The controller 160 can thusselectively illuminate lighted indicators 164 integrated into the EEGheadset 102 adjacent electrodes determined to be in poor contact withthe user's skin in order to visually indicate to the EEG testadministrator—directly on the EEG headset 102—which electrodes requireadjustment, such as in addition to transmitting an electrode adjustmentprompt to the external device associated with the EEG testadministrator. (The controller 160 can also selectively change colors ofor selectively adjust illumination patterns (e.g., blinking patterns) ofthese lighted indicators 164 to indicate their contact states.) Thecontroller 160 can similarly visually communicate to the user wearingthe EEG headset 102—such as while sitting before a mirror—whichelectrodes require correction, and the user can depress regions of thesupport structure near illuminated lighted indicators 164 (or red orblinking lighted indicators) directly to correct skin contact at theseelectrodes.

In the foregoing implementations, when lighted indicator 164 (e.g., anLED) adjacent an electrode is activated, electromagnetic radiationoutput by the lighted indicator 164 may produce an extraphysiologicartifact in the signal output by its corresponding (i.e., adjacent)electrode. However, the reference and sense signals collected by thereference and sense electrodes, respectively may include substantiallysimilar indicator-based extraphysiologic artifacts, which may be excludefrom each composite sense signal via common-mode rejection when the rawreference signal is subtracted from raw sense signals at the signalprocessor 150 in Block S131, as described above.

However, the controller 160 can modify a state of any other one or morelighted indicators 164 integrated into the EEG headset 102 in order tovisually indicate the contact state or contact quality of each electrodeon the user's skin.

8.7 User-Directed Notifications

In one variation, the controller 160 (or a native EEG test applicationexecuting on a computing device carried by or accessible to the user)can also serve a prompt to correct skin contact at an electrode directlyto the user. For example, the controller 160 (or the native EEG testapplication) can implement methods and techniques described above toupdate a lighted indicator integrated into the EEG headset 102 toindicate poor contact at a particular electrode adjacent the lightedindicator and then push a prompt to correct the particular electrode tothe user's smartphone, such as by depressing the particular electrode orby adjusting a headband supporting the particular electrode on theuser's head. While looking at a mirror, the user can thus adjust theparticular electrode accordingly. The controller 160 can thus serve aprompt directly to the user in order to reduce a burden on the EEG testadministrator to monitor the user or if the user is completing an EEGtest without the aid of an EEG test administrator (e.g., while at home).

The controller 160 can also selectively serve electrode adjustmentprompts to one of the user and the EEG test administrator based on atype of adjustment needed. For example, the controller 160 can serveprompts to correct electrodes exhibiting moderate contact quality—suchas characterized by contact quality oscillating between proper andimproper and improper for no more than ten seconds per twenty-secondinterval—to the user. In this example, the user can thus manuallydepress such an electrode with her finger to correct contact with theuser's skin. However, in this example, the controller 160 can serveprompts to correct electrodes exhibiting poor contact quality—such ascharacterized by improper contact for more than ten seconds pertwenty-second interval—exclusively to the EEG test administrator, assuch poor contact quality may require the EEG test administrator toclean the user's skin or replace an electrode tip.

However, the controller 160 (or native EEG test application) canimplement any other method or technique to serve electrode adjustmentprompts directly to the user.

9. Setup

In one variation, the controller 160 (and/or the native EEG testapplication executing on the external device) implements the foregoingmethods and techniques to indicate to the EEG test administrator (or tothe user) the contact state of each electrode substantially in real-timeas the EEG headset 102 is placed on the user's head and adjusted inpreparation for an EEG test. In this variation, the controller 160 canthus provide electrode contact feedback to the EEG test administratorsubstantially in real-time to enable the EEG test administrator toachieve proper contact between the user's skin and all electrodes in theEEG headset 102 before beginning the EEG test and moving physically awayfrom the user, such as to prepare another user for another EEG test witha similar EEG headset.

In this variation, prior to installation of the EEG headset 102 on theuser's head the controller 160 (or the native EEG test application, or aremote computer system) can also predict adjustments for the supportstructure (e.g., each headband) in the EEG in order to achieve properskin contact across each electrode. For example, during setup, the EEGtest administrator can enter the user's head shape and head side intothe native EEG test application, such as through dropdown menusenumerating qualitative head shapes (e.g., square, round, diamond,triangular, oblong, and oval) and qualitative head sizes (small, medium,and large). The native EEG test application can then retrieve predefinedsetup instructions corresponding to the combination of head shape andhead size entered by the EEG test administrator, such as a length oradjustment position of each headband within the EEG headset 102 toaccommodate the user's head shape and size. The native EEG testapplication can then serve these instructions to the EEG testadministrator through a display integrated into the device executing thenative EEG test application.

In the foregoing example, during setup, the EEG test administrator canalso enter the user's hair type, quality, and quantity into the nativeEEG test application, such as through dropdown menus enumeratingqualitative hair types (e.g., none, straight, wavy, curly, kinky, anddreadlocks) qualitative hair thicknesses (e.g., thin, full, and thick);and qualitative hair quantity (none, bald above crown, buzz, short,moderate, or long). The native EEG test application can then retrievepredefined contact insert types for each electrode based on the user'shair type, quality, and quantity entered by the EEG test administrator,such as a callout for one of: an elastic bristle insert; a rigid pronginsert; a flat contact disk insert; and a domed contact disk insert;etc. for each electrode. The native EEG test application can then servethese contact insert type callouts to the EEG test administrator throughthe device executing the native EEG test application.

Once the EEG headset 102 is placed on the user's head and adjusted toachieve proper skin contact across all electrodes in the EEG headset102, as confirmed by the controller 160 in Blocks S126 and S136, thecontroller 160 (or the native EEG test application, or a remote computersystem) can store headband adjustments and/or contact insert types foreach electrode in an electronic profile for the user. For example, theremote computer system can store this configuration as a targetconfiguration for the user in the user's electronic profile. If resultsof the subsequent EEG test indicate suitable skin contact acrosselectrodes in the EEG headset 102, such as less than 5% improper contactacross all electrodes for the entire duration of the EEG test, theremote computer system can also update this configuration for the userbased on adjustments made to the EEG headset 102 or to contact inserttypes at each electrode during the EEG test to improve contact qualityat each electrode. During setup of additional EEG tests in the future,the controller 160 (or the native EEG test application, or a remotecomputer system) can serve this headset configuration to an EEG testadministrator tasked with configuring an EEG headset for the user forthese future EEG tests. Furthermore, during setup of additional EEGtests in the future, the controller 160 (or the native EEG testapplication, or a remote computer system) can serve suggestions—to theEEG test administrator—for taking special care in placing certainelectrodes on the user based on poor contact quality at these electrodesduring past EEG tests.

However, the controller 160 (or the native EEG test application, or aremote computer system) can feed data—collected during setup andexecution of an EEG test at a user—forward to setup and execution of alater EEG test in any other way in order to reduce setup time for thelater EEG test and/or to the quality of data collected during the laterEEG test.

10. Signal Annotation

As shown in FIG. 1, one variation of the method S100 further includesBlock S150, which recites: over a period of time, writing a digitalrepresentation of the first composite sense signal to a digital file;and annotating the digital representation of the first composite sensesignal with contact states of the driven electrode 110, the referenceelectrode 120, and the first sense electrode 131 over the period oftime. Generally, in Block S150, the controller 160 can record compositesense signals read from each sense electrode 131 to a digital file andcan annotate each composite sense signal in the digital file with thecontact states or contact state changes throughout the EEG test overwhich these composite sense signals were recorded. In particular, duringoperation (e.g., during an EEG test), the controller 160 can flag orannotate each sense channel (e.g., a data stream read from the referenceelectrode 120 and unique data streams generated from raw sense signalsread from each sense electrode 131) with its contact status (e.g., acontact loss status and/or a proper contact status), such as for eachsampling period or for each change in the contact state of thecorresponding electrode.

For example, in Block S122 or S124, if the signal processor 150determines that the reference electrode 120 or the driven electrode 110has lost contact with the user's skin during a particular period of timeduring an EEG test, the controller 160 can annotate a data stream readfrom each sense electrode 131 with a “discard” label, as these datastreams are unreliable during this particular period due to lack ofproper skin contact at the drive and reference electrode. In anotherexample, in Block S132, if the signal processor 150 determines that 18of 19 sense electrodes are in proper contact with the user's skin butthat a 19^(th) sense electrode 131 has lost contact with the user's skinduring a particular period of time during the EEG test, the controller160 can annotate a data stream from the 19^(th) sense electrode 131 witha “contact lost” label to indicate that these data in the 19^(th) datastream are unreliable during this particular period.

Alternatively, in Block S150 the controller 160 can stream these datastreams to a remote computer system, such as to the EEG testadministrator's smartphone over wireless communication protocol, to adesktop computer connected to the EEG headset 102, or to a remotecomputer system (e.g., a remote server) over the Internet. The EEG testadministrator's smartphone, the desktop computer connected to the EEGheadset 102, or the remote computer system can then implement similarmethods and techniques to store these data streams in a digital file andto associate these data streams with contact qualities of theircorresponding electrodes.

11. Dynamic Drive Signal

As shown in FIG. 1, one variation of the method S100 includes:outputting a drive signal through a driven electrode 110 in Block S110,the drive signal including an alternating-current component oscillatingat a reference frequency and a direct-current component; reading areference signal from a reference electrode 120 proximal the drivenelectrode no in Block S120; in response to the raw reference signalincluding a first signal component oscillating at the referencefrequency, confirming proper contact between the user's skin and thedriven electrode 110 and between the user's skin and the referenceelectrode 120 in Block S126; reading a sense signal from each senseelectrode 131 in a set of sense electrodes in Block S130; in response toeach sense signal read from a first subset of sense electrodes in theset of sense electrodes at a first time including a third signalcomponent oscillating at the reference frequency, confirming propercontact between the user's skin and the sense electrode 131 in BlockS136. In this variation, the method S100 further includes Block S160,which recites: for each sense electrode 131 in the first subset of senseelectrodes, calculating raw composite sense signal by subtracting theraw reference signal from the sense signal output by the sense electrode131 at the first time; calculating a first linear combination of thefirst set of raw composite signals; summing the first linear combinationand a direct-current component of the drive signal at approximately thefirst time to calculate a second direct-current value for the drivesignal; and at a second time succeeding the first time, shifting thedrive signal to the second direct-current value.

Generally, in this Block S160, the controller 160 calculates a new DCcomponent of the drive signal based on a linear combination (e.g., anaverage of) (raw or composite) sense signals read from each senseelectrode 131 confirmed to be in proper contact with the user's skin inorder to maintain the center voltage of the drive signal at a center ofthe dynamic range of the system over time, such as to compensate for theoutput voltage of a battery 170 or other power supply integrated intothe EEG headset 102. In particular, the output voltage of the battery170 (or other power supply) supplying power to the controller 160, thesignal processor 150, and electrodes within the EEG headset 102 maydictate a dynamic range of the signal processor 150 (e.g., the dynamicrange of the ADC). Furthermore, because the output voltage of thebattery 170 may change as the battery 170 is discharged, as thetemperature of the battery 170 changes, as the battery 170 ages, or as aload on the battery 170 changes, etc. over time, the dynamic range ofthe signal processor 150 may also change over time. Therefore, to ensurethat raw reference and sense signals read by the signal processor 150remain substantially centered within the dynamic range of ADC over time,the controller 160 can recalculate the DC component of the drive signalover time. The signal generator 140 then modifies the drive signaldynamically during an EEG test according to the new DC componentcalculated by the controller 160. The controller 160 and the signalgenerator 140 can repeat this process at or after each sampling periodduring operation of the EEG headset 102.

In one implementation, at startup (e.g., at the beginning of an EEGtest), the signal generator 140 generates a drive signal that includes aDC component at a voltage half of the nominal battery voltage. In oneexample in which the EEG headset 102 includes a battery configured tooutput a nominal 3.3 Volts to the signal processor 150 and to amplifiersat each reference and sense electrode 131, at startup, the signalgenerator 140 can output a drive signal containing a 1.65V DC componentto the driven electrode 110. For each subsequent sampling period, thecontroller 160 can: calculate an linear combination of composite digitalsense signals read by the signal processor 150 (from which the rawreference signal read from the reference electrode 120 has already beensubtracted in Block S131, as described above); transform the linearcombination into a composite voltage value; and then sum this compositevoltage value and the voltage of the DC component of the drive signaloutput during the current (or preceding) sampling period to calculate anew DC voltage for the drive signal at the next sampling period. Thecontroller 160 can pass each new DC voltage of the drive signal to thesignal generator 140, and the signal generator 140 can shift the drivesignal to this new DC voltage during the next sampling period. Thecontroller 160 can repeat this process to calculate a new DC voltage ofthe drive signal—approximately centered within the dynamic range of thesystem, as dictated by the nominal voltage of the battery 170—for eachsubsequent sampling period during operation of the EEG headset 102.

In the foregoing implementation, because signals read from senseelectrodes determined to be in improper contact with the user's skin maybe unreliable, the controller 160 can calculate the linear combinationof composite digital sense signals originating exclusively from senseelectrodes determined to be in proper contact with the user's skinduring a current (or last) sampling period. The linear combination ofthese composite digital sense signals can thus represent the combined(e.g., average) voltage across sense electrodes in proper contact withthe user's skin during the current (or last) sampling period, less thevoltage of the reference signal during the current (or last) samplingperiod. By then summing a DC voltage represented by the linearcombination with the DC voltage of the drive signal during the current(or last) sampling period, the controller 160 can calculate a new DCvoltage—approximately aligned with the center voltage of the ADC—for thedrive signal. The signal generator 140 can then shift the drive signalto this new DC voltage during the next sampling period.

The controller 160 can repeat this process for each sampling period (orfollowing a set of sampling periods). In particular, the controller 160can track changes in skin contact quality at each electrode anddynamically adjust a subset of composite digital sense signals combinedto calculate a composite (e.g., average) digital voltage valueaccordingly for each subsequent sampling period. For example, in BlockS160, after updating the DC component of the drive signal at a firsttime, the controller 160 can determine improper contact between theuser's skin and sense electrodes in a second subset of sense electrodesin Block S132 in response to each raw sense signal read from a secondsubset of sense electrodes in the set of sense electrodes at the firsttime excluding the third signal component oscillating at the referencefrequency (or in response to each composite sense signal read from asecond subset of sense electrodes in the set of sense electrodes at thefirst time including the third signal component oscillating at thereference frequency), wherein the second subset of sense electrodes isdistinct from the first subset of sense electrodes.

In Block S160, the controller 160 can then: identify a second subset ofsense electrodes in the set of sense electrodes in proper contact withthe user's skin at the second time, the second subset of senseelectrodes different from the first subset of sense electrodes; for eachsense electrode 131 in the second subset of sense electrodes, calculatea voltage difference, in a second set of voltage differences, between avoltage of the raw reference signal and a voltage of a sense signaloutput by the sense electrode 131 at the second time; calculate a secondlinear combination of the second set of voltage differences; sum thesecond linear combination and a voltage of the direct-current componentof the drive signal at approximately the second time to calculate athird direct-current voltage of the drive signal; and at a third timesucceeding the second time, shift the direct-current component of thedrive signal to the third direct-current voltage.

In particular, the signal processor 150 can continuously sample thesense electrodes. During each scan cycle, the controller can define asubset of sense electrodes in proper contact with the user's skin andthen flag (raw or composite) sense signals read from each senseelectrode in this subset of sense electrodes for calculation of the DCcomponent of the drive signal output by the driven electrode in the nextscan cycle.

Furthermore, when the driven electrode 110 and/or the referenceelectrode 120 are determined to have lost contact with the user's skin,the controller 160 can maintain a last DC component of the drive signalunchanged. In particular, in response to determination of impropercontact between the user's skin and one of the driven electrode no andthe reference electrode 120, the controller 160 can maintain thedirect-current component of the drive signal substantially unchangeduntil proper contact between the user's skin and the driven electrode noand between the user's skin and the reference electrode 120 areconfirmed.

Alternatively, in this variation, for the signal processor 150 thatexhibits a dynamic range less than the nominal voltage output of thebattery 170, at startup, the signal generator 140 can generate a drivesignal that includes a DC component at a voltage (above the batteryground) half of the dynamic range of the signal processor 150. Thecontroller 160 can then implement averaging techniques as describedabove to calculate a new drive signal DC voltage that centers theaverage outputs of the sense electrodes (and the reference electrode120) for the current (or last) sampling period within the dynamic rangeof the signal processor 150.

For example, the controller 160 can: calculate a linear combination ofcomposite digital sense signals read (from sense electrodes determinedto be in proper contact with the user's skin) by the signal processor150; sum this linear combination and a digital value representing thevoltage of the DC component of the drive signal output during thecurrent (or preceding) sampling period to calculate a composite (e.g.,average) digital center signal value for the current sampling period.The controller 160 can then: calculate a digital difference bysubtracting this composite digital center signal from the center of thedynamic range of the signal processor 150 (e.g., “127” for an 8-bit ADCoutputting digital values between 0 and 255 in each sense channel);transform this digital difference value into a voltage difference; andadd this voltage difference to the current (or last) DC voltage of thedrive signal to calculate a new DC voltage for the drive signal at thenext sampling period. The signal generator 140 can then implement thisDC voltage accordingly at the next sampling period, as described above.

The signal generator 140 can therefore output a drive signal including aDC component that follows the sense signals (and the raw referencesignal) collected by the sense electrodes (and by the referenceelectrode 120). The signal generator 140 can combine the dynamic DCcomponent with a static AC component, such as a sinusoidal, 2.0 Hz, 17millivolt peak-to-peak AC signal, as described above. However, thesignal generator 140 can output a drive signal including DC and ACcomponents at any other voltage and—for the AC component—oscillating atany other frequency and according to any other waveform. Furthermore,the controller can implement the foregoing methods and techniques toprocess raw or composite analog sense signals to calculate a new DCcomponent of the drive signal for each subsequent scan cycle.

12. Motion Tracking

In one variation, the EEG headset 102 further includes an accelerometer,gyroscope, compass, and/or other motion sensor, such as arranged in thehousing described above. In this variation, the controller 160 cansample the motion sensor during operation (e.g., during an EEG test),correlate an output of the sensor with a magnitude and/or direction ofmotion of the user's head, and set an excess motion flag in response tothe magnitude of motion of the user's head exceeding a threshold motion(e.g., acceleration) magnitude. The wireless communication module 162can then push an excess motion notification to the external devicesubstantially in real-time based on the excess motion flag. For example,the controller 160 can generate a notification including a textualprompt to quell the user, such as reciting, “The user is exceeding amotion limit for the current EEG test,” and the wireless communicationmodule 162 can push this notification to the external device, asdescribed above, for substantially immediate response by the EEG testadministrator. Based on the notification, the EEG test administrator canthen return to and quiet the user.

Generally, movements by the user during the EEG test may createartifacts in the EEG data collected during the EEG test and/or may causean electrode to lose contact with the user's skin. The EEG headset 102can therefore sample the motion sensor during the EEG test, characterizethe outputs of the motion sensor, and notify an EEG test administratorif the user's motion exceeds a motion limit, such as a motion limitcharacterized by relatively high risk of data artifacts or by relativelyhigh risk of loss of electrode contact. The EEG headset 102 cantherefore provide guidance to the EEG test administrator—through theexternal device or through an audible or visual indicator on the EEGheadset 102—to minimize user motion that may create artifacts in EEGtest data or lead to low-quality EEG data collected during the EEG test.

In one implementation, the EEG headset 102 includes an accelerometer,and the controller 160 retrieves acceleration limits for various motiontypes specified for an upcoming EEG test and generates excess motionnotifications while the EEG test is in process based on these specifiedacceleration limits. For example, the controller 160 can access adatabase in which a maximum (X-, Y-, and Z-axis) composite accelerationfor each of multiple motion types are specified for available EEG tests,including a walking-type motion characterized by accelerations below 0.5Hz, a fidgeting motion characterized by accelerations between 0.5 Hz and1.0 Hz, a talking-type motion characterized by accelerations between 1.0Hz and 2.0 Hz, and a blinking-type motion characterized by accelerationsgreater than 2.0 Hz, etc. In this example, the database can definemoderate acceleration limits for the walking-, fidgeting-, talking-, andblinking-type motions for a general seated EEG test, whereas thedatabase can define relatively low acceleration limits for blinking-typemotions for frontal lobe tests and relatively high acceleration limitsfor temporal lobe tests. Furthermore, in this example, for a generalwalking EEG test, the database can define a relatively high accelerationlimit for walking-type motions and a relatively low acceleration limitfor talking-type motions. The EEG headset 102 can therefore compareacceleration values output by the accelerometer to EEG test-specificmotion limits to identify instances of excess motion, and the EEGheadset 102 can generate and distribute notifications to the EEG testadministrator (or directly to the user) accordingly.

Alternatively, the EEG headset 102 can implement generic motion limitsacross all EEG tests and can selectively activate and deactivate flagsfor excess motion types based on a type of the current EEG test. Forexample, when a general walking EEG test is underway, the EEG headset102 can deactivate motion limits for walking-type and fidgeting-typemotions but maintain motion limits for talking-type and blinking-typemotions. However, in this example, when a seated frontal lobe test isunderway, the EEG headset 102 can activate motion limits for allwalking-, fidgeting-, talking-, and blinking-type motions.

The EEG headset 102 can additionally or alternatively notify the userdirectly of excess motion (and/or of electrode contact loss events, asdescribed above), such as through a speaker integrated into the EEGheadset 102 or through an external device (e.g., a smartphone, a tablet)carried or accessible directly by the user. However, the EEG headset 102can implement any other method or technique to notify the EEG testadministrator and/or the user of excess user motion and of electrodecontact loss events. The EEG headset 102 can also annotate EEG datacollected during the EEG test with motion data recorded through themotion sensor during the EEG test, such as by noting periods in eachsense channel that corresponds in time to periods of over-activity orexcessive motion by the user.

13. Remote Signal Processing

In one variation, the EEG headset 102 transmits electrode data (e.g.,the digital reference signal and composite digital sense signals) to theremote external device substantially in real-time, and the externaldevice implements methods and techniques described above to transformthese electrode data into electrode contact qualities and to issuenotifications—through its integrated display—to correct instances ofpoor electrode contact.

The systems and methods described herein can be embodied and/orimplemented at least in part as a machine configured to receive acomputer-readable medium storing computer-readable instructions. Theinstructions can be executed by computer-executable componentsintegrated with the application, applet, host, server, network, website,communication service, communication interface,hardware/firmware/software elements of a user computer or mobile device,wristband, smartphone, or any suitable combination thereof. Othersystems and methods of the embodiment can be embodied and/or implementedat least in part as a machine configured to receive a computer-readablemedium storing computer-readable instructions. The instructions can beexecuted by computer-executable components integrated bycomputer-executable components integrated with apparatuses and networksof the type described above. The computer-readable medium can be storedon any suitable computer readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component can bea processor but any suitable dedicated hardware device can(alternatively or additionally) execute the instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

I claim:
 1. A method for testing contact quality of electrical-biosignalelectrodes comprising: outputting a drive signal through a drivenelectrode, the drive signal comprising an alternating-current componentoscillating at a reference frequency and a direct-current component;reading a reference signal from a reference electrode proximal thedriven electrode; in response to the reference signal excluding a firstsignal component oscillating at the reference frequency and excluding asecond signal component oscillating at an ambient frequency, determiningthat the reference electrode is in improper contact with a user's skin;in response to the reference signal excluding the first signal componentoscillating at the reference frequency and comprising the second signalcomponent oscillating at the ambient frequency, determining that thedriven electrode is in improper contact with the user's skin; reading afirst sense signal from a first sense electrode; in response to thereference signal comprising the first signal component oscillating atthe reference frequency and in response to the first sense signalexcluding a third signal component oscillating at the referencefrequency, determining that the first sense electrode is in impropercontact with the user's skin; and in response to determination ofimproper contact between the user's skin and one of the drivenelectrode, the reference electrode, and the first sense electrode,generating an electrode adjustment prompt.
 2. The method of claim 1:wherein reading the first sense signal from the first sense electrodecomprises scanning a set of sense electrodes comprising the first senseelectrode and a second sense electrode—the set of sense electrodes, thedriven electrode, and the reference electrode integrated into anelectroencephalography headset worn by the user; and further comprising:reading a second sense signal from the second sense electrode proximalthe first sense electrode; and in response to the reference signalcomprising the first signal component oscillating at the referencefrequency and in response to the second sense signal comprising thethird signal component oscillating at the reference frequency,determining that the second sense electrode is in proper contact withthe user's skin.
 3. The method of claim 2, further comprising:identifying a first subset of sense electrodes in the set of senseelectrodes in proper contact with the user's skin at a first time; foreach sense electrode in the first subset of sense electrodes,calculating a composite sense signal, in a first set of composite sensesignals, by subtracting the reference signal from a raw sense signaloutput by the sense electrode at the first time; calculating a firstlinear combination of the first set of composite sense signals; summingthe first linear combination and the direct-current component of thedrive signal at approximately the first time to calculate a seconddirect-current value of the drive signal; and at a second timesucceeding the first time, shifting the direct-current component of thedrive signal to the second direct-current value.
 4. The method of claim3, further comprising: identifying a second subset of sense electrodesin the set of sense electrodes in proper contact with the user's skin atthe second time, the second subset of sense electrodes different fromthe first subset of sense electrodes; for each sense electrode in thesecond subset of sense electrodes, calculating a composite sense signal,in a second set of composite sense signals, by subtracting the referencesignal and from a raw sense signal output by the sense electrode at thesecond time; calculating a second linear combination of the second setof composite sense signals; summing the second linear combination andthe direct-current component of the drive signal at approximately thesecond time to calculate a third direct-current value of the drivesignal; and at a third time succeeding the second time, shifting thedirect-current component of the drive signal to the third direct-currentvalue.
 5. The method of claim 2, wherein generating the electrodeadjustment prompt comprises: in response to determination of impropercontact between the user's skin and the first sense electrode,illuminating a first lighted indicator, arranged in theelectroencephalography headset adjacent the first sense electrode, in afirst color to indicate improper contact between the user's skin and thefirst sense electrode; and in response to determination of propercontact between the user's skin and the second sense electrode,illuminating a second lighted indicator, arranged in theelectroencephalography headset adjacent the second sense electrode, in asecond color to indicate proper contact between the user's skin and thesecond sense electrode.
 6. The method of claim 1, wherein generating theelectrode adjustment prompt comprises: tracking a duration of acontiguous period of time during which the first sense electrode isdetermined to be in improper contact with the user's skin; andtransmitting an electronic notification prompting adjustment of thefirst sense electrode to an external computing device accessible by anelectroencephalography test administrator in response to the duration ofthe contiguous period of time exceeding a threshold duration.
 7. Themethod of claim 6: wherein reading the first sense signal from the firstsense electrode comprises scanning through a set of sense electrodescomprising the first sense electrode, the set of sense electrodes, thedriven electrode, and the reference electrode integrated into anelectroencephalography headset worn by the user; and further comprising:tracking a total duration of time during which sense electrodes acrossthe set of sense electrodes are determined to be in improper contactwith the user's skin; and transmitting, to the external computingdevice, a second electronic notification prompting restart of anelectroencephalography test current at the electroencephalographyheadset in response to the total duration of time exceeding a secondthreshold duration.
 8. The method of claim 1: wherein determining thatthe driven electrode is in improper contact with the user's skin anddetermining that the reference electrode is in improper contact with theuser's skin comprise: decomposing the reference signal into a first setof oscillating signal components; determining that the referenceelectrode is in improper contact with the user's skin in response to thefirst set of oscillating signal components excluding the first signalcomponent oscillating at the reference frequency and excluding thesecond signal component oscillating at approximately 60 Hz; anddetermining that the driven electrode is in improper contact with theuser's skin in response to the first set of oscillating signalcomponents excluding the first signal component oscillating at thereference frequency and comprising the second signal componentoscillating at approximately 60 Hz; and further comprising determiningthat the driven electrode and the reference electrode are in propercontact with the user's skin in response to the first set of oscillatingsignal components comprising the first signal component oscillating atthe reference frequency. wherein reading the first sense signal from thefirst sense electrode comprises reading a first raw sense signal fromthe first sense electrode in response to determining that the drivenelectrode and the reference electrode are in proper contact with theuser's skin; wherein determining that the first sense electrode is inimproper contact with the user's skin comprises, in response todetermination that the driven electrode and the reference electrode arein proper contact with the user's skin: subtracting the reference signalfrom the first raw sense signal to calculate a composite sense signal;decomposing the composite sense signal into a second set of oscillatingsignals; and determining that the first sense electrode is in impropercontact with the user's skin in response to the second set ofoscillating signal components comprising the third signal componentoscillating at the reference frequency; and further comprising, inresponse to determination that the driven electrode and the referenceelectrode are in proper contact with the user's skin, determining thatthe first sense electrode is in proper contact with the user's skin inresponse to the second set of oscillating signal components excludingthe third signal component oscillating at the reference frequency. 9.The method of claim 1, further comprising: over a period of time,writing a digital representation of the first sense signal to a digitalfile; and annotating the digital representation of the first sensesignal with contact states of the driven electrode, the referenceelectrode, and the first sense electrode over the period of time. 10.The method of claim 1: wherein reading the drive signal from the drivenelectrode, reading the reference signal from the reference electrode,and reading the first sense signal from the first sense electrodecomprise scanning a set of electrodes integrated into anelectroencephalography headset worn by the user, the set of electrodescomprising the driven electrode, the reference electrode, and the firstsense electrode; and wherein generating the electrode adjustment promptcomprises: generating an electronic notification comprising a prompt tocorrect contact between a particular electrode in the set of electrodes;inserting a virtual map of locations of the electrodes in theelectroencephalography headset into the electronic notification; andindicating the particular electrode within the virtual map.
 11. Themethod of claim 1: wherein reading the first sense signal from the firstsense electrode comprises: executing an electroencephalography test atan electroencephalography headset worn by the user; and sequentiallyreading sense signals from sense electrodes in a set of sense electrodesintegrated into the electroencephalography headset, the set of senseelectrodes comprising the first sense electrode and a second senseelectrode; wherein generating the electrode adjustment prompt comprises,in response to determination of improper contact between the user's skinand the first sense electrode, generating the electrode adjustmentprompt specifying adjustment of the first sense electrode defined asrelevant for a type of the electroencephalography test; and furthercomprising disregarding determination of improper contact between theuser's skin and the second sense electrode defined as irrelevant for thetype of the electroencephalography test.
 12. The method of claim 1:wherein reading the drive signal from the driven electrode, reading thereference signal from the reference electrode, and reading the firstsense signal from the first sense electrode comprise scanning a set ofelectrodes integrated into an electroencephalography headset worn by theuser, the set of electrodes comprising the driven electrode, thereference electrode, and the first sense electrode; and whereingenerating the electrode adjustment prompt comprises, in response todetection of improper contact between the first sense electrode and theuser's skin: predicting an adjustment mode for theelectroencephalography headset to improve contact between the firstsense electrode and the user's skin based on a virtual model of amechanical structure of the electroencephalography headset; inserting adescription of the adjustment mode into an electronic notification; andat a first time, transmitting the electronic notification to a localcomputing device.
 13. An electrical biosignal acquisition system 100comprising: a driven electrode electrically configured to contact skinof a user remotely from an area of interest; a signal generatorconfigured to output a drive signal oscillating at a reference frequencyabout a center voltage into the user via the driven electrode; areference electrode configured to contact skin of the user remotely fromthe area of interest and to detect a reference signal; a first senseelectrode configured to contact skin of the user at the area of interestand to detect a first sense signal from the area of interest; a supportstructure configured to support the driven electrode, the referenceelectrode, and the first sense electrode on the user; and a the signalprocessor configured to: transform absence of a first signal componentoscillating at the reference frequency in the reference signal andabsence of a second signal component oscillating at an ambient frequencyin the reference signal into confirmation that the reference electrodeis in improper contact with the user's skin; transform absence of thefirst signal component oscillating at the reference frequency andpresence of the second signal component oscillating at the ambientfrequency in the reference signal into confirmation that the drivenelectrode is in improper contact with the user's skin; and to transformconfirmation that the reference electrode is in proper contact with theuser's skin, confirmation that the driven electrode is in proper contactwith the user's skin, and absence of a third signal componentoscillating at the reference frequency from the first sense signal intoconfirmation that the first sense electrode is in improper contact withthe user's skin.
 14. The electrical biosignal acquisition system ofclaim 13, further comprising a controller configured to generate aprompt to adjust the support structure in response to confirmation ofimproper contact between the user's skin and one of the drivenelectrode, the reference electrode, and the first sense electrode and totransmit the prompt to a remote computing device.
 15. The electricalbiosignal acquisition system of claim 13, wherein the first senseelectrode comprises a dry electroencephalography electrode comprising: asubstrate; a set of electrically-conductive prongs extending from afirst side of the substrate; and an amplifier coupled to the substrateopposite the set of prongs and configured to amplify an electricalsignal detected by the set of prongs.
 16. A method for testing contactquality of electrical-biosignal electrodes comprising: outputting adrive signal through a driven electrode, the drive signal comprising analternating-current component oscillating at a reference frequency and adirect-current component; reading a reference signal from a referenceelectrode proximal the driven electrode; in response to presence of afirst signal component oscillating at the reference frequency in thereference signal, confirming proper contact between the user's skin andthe driven electrode and between the user's skin and the referenceelectrode; reading a raw sense signal from each sense electrode in a setof sense electrodes; in response to each sense signal read from a firstsubset of sense electrodes in the set of sense electrodes at a firsttime comprising a third signal component oscillating at the referencefrequency, confirming proper contact between the user's skin and thesense electrode; for each sense electrode in the first subset of senseelectrodes, calculating a composite sense signal, in a first set ofcomposite sense signals, by subtracting the reference signal from a rawsense signal output by the sense electrode at the first time;calculating a first linear combination of the first set of compositesense signals; summing the first linear combination and thedirect-current component of the drive signal at approximately the firsttime to calculate a second direct-current value of the drive signal; andat a second time succeeding the first time, shifting the direct-currentcomponent of the drive signal to the second direct-current value. 17.The method of claim 16, further comprising: in response to the referencesignal excluding a first signal component oscillating at the referencefrequency and excluding a second signal component oscillating at anambient frequency, determining that the reference electrode is inimproper contact with a user's skin; and in response to the referencesignal excluding the first signal component oscillating at the referencefrequency and comprising the second signal component oscillating at theambient frequency, determining that the driven electrode is in impropercontact with the user's skin; and in response to determination ofimproper contact between the user's skin and one of the driven electrodeand the reference electrode, maintaining the direct-current component ofthe drive signal unchanged until proper contact between the user's skinand the driven electrode and between the user's skin and the referenceelectrode are confirmed.
 18. The method of claim 17, further comprising:in response to determination of improper contact between the user's skinand one of the driven electrode, the reference electrode, and a senseelectrode in the set of sense electrodes, generating an electronicnotification comprising an electrode adjustment prompt; and transmittingthe electronic notification to an external computing device accessibleby a biosignal test administrator.
 19. The method of claim 16, furthercomprising, in response to each sense signal read from a second subsetof sense electrodes in the set of sense electrodes at the first timeexcluding the third signal component oscillating at the referencefrequency, determining improper contact between the user's skin andsense electrodes in the second subset of sense electrodes, the secondsubset of sense electrodes distinct from the first subset of senseelectrodes.
 20. The method of claim 16, further comprising: identifyinga second subset of sense electrodes in the set of sense electrodes inproper contact with the user's skin at the second time, the secondsubset of sense electrodes different from the first subset of senseelectrodes; for each sense electrode in the second subset of senseelectrodes, calculating a composite sense signal, in a second set ofcomposite sense signals, by subtracting the reference signal from a rawsense signal output by the sense electrode at the second time;calculating a second linear combination of the second set of compositesense signals; summing the second linear combination and thedirect-current component of the drive signal at approximately the secondtime to calculate a third direct-current value of the drive signal; andat a third time succeeding the second time, shifting the direct-currentcomponent of the drive signal to the third direct-current value.